The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel and ignited in a combustor for generating hot combustion gases. The hot gases flow downstream through several turbine stages which extract energy therefrom for powering the compressor, and providing output work in the exemplary form of powering a fan in a turbofan engine configured for powering an aircraft in flight.
Since the hot combustion gases are first generated in the combustor, the combustor and its associated components must be specifically configured for withstanding the high temperatures of combustion and providing a suitable useful life. The various combustor components are typically cooled during operation by channeling therethrough relatively cool air bled from the compressor discharge.
A typical combustor includes radially outer and inner annular liners attached at forward ends to an annular combustor dome. The dome is a thin plate extending radially between the two liners and may be configured for supporting a single row of carburetors in a single annular design, or two carburetor rows in a double annular design, or even more rows. Nevertheless, each carburetor typically includes an air swirler which swirls and mixes air with fuel injected from a respective fuel injector. The fuel and air mixture is ignited and generates the hot combustion gases immediately downstream from the dome.
The dome is typically protected from the high heat of combustion by individual heat shields or splashplates disposed inside the dome at the aft end of each swirler. The heat shields generally have four sides or edges and collectively form an annular heat shield inside the dome for each row of carburetors.
Modem aircraft gas turbine engines are designed for long life with minimal repair or maintenance requirements. The air swirler, combustor dome, and combustor liners are well cooled during operation and have correspondingly long useful lives. However, the individual heat shields in view of their fundamental function of protecting the combustor dome from the high heat generated during combustor operation, are typically replaced several times during the useful life of the combustor and engine.
The cost of replacing the heat shields in a typical maintenance outage scheduled therefor is substantial in view of the large number of heat shields which must be replaced in the outage; the complexity of the mounting configuration therefor; the complexity of the removal process; and the complexity of the assembly process.
For example, in a typical combustor design the heat shields are assembled through a corresponding aperture in the dome in an annular joint therewith, as well as in a corresponding joint with the air swirler. These joints are typically brazed for creating a permanent connection with the dome.
Since the dome, heat shield, and swirler represent three components which must be assembled together and brazed, they are subject to inadvertent misassembly thereof which becomes permanent upon brazing. Excessive misalignment requires disassembly of the components and suitable correction, with a corresponding cost associated therewith.
Since the swirler and combustor dome include a multitude of small cooling holes therefor, some of those holes are subject to inadvertent plugging during the brazing operation due to their close proximity to the braze joints.
In order to repair the combustor after extended use in a maintenance outage, or to correct misassembly during initial manufacture, a brazed joint must be suitably broken for disassembling the components. Since the heat shield is a consumable or replaceable component it may be machined or cut as required without regard to its cost. However, the machining operation must be done with sufficient care to prevent damage to the dome or the air swirler which are designed for long life. The repair process, therefore, requires substantial time to individually machine and disassemble each of the carburetors from the dome, and then reassemble and re-braze the repaired assembly thereof.
Accordingly, it is desired to provide a combustor having an improved heat shield assembly with the combustor dome for improving the assembly and disassembly processes thereof.
A combustor baffle includes an outer tube with external threads and a heat shield at opposite ends thereof. An inner tube is disposed inside the outer tube in a unitary assembly therewith. The outer tube is retained in a combustor dome by a retention nut, and the inner tube supports an air swirler with a brazed joint therewith. The brazed joint permits sacrifice of the baffle during disassembly for access to the threaded joint for final disassembly without damage to the dome or air swirler.